Controller and Control System That Manages Event Occurrence History Utilizing a Flash Chain of Event History Data

1. A control device for controlling a control target device, the control device comprising: hash value circuitry configured to calculate a first hash value on a basis of event history data of an event that occurs during operation of the control device; communicator circuitry configured to transmit the first hash value to a first another controller disposed external to the control device and receive a second hash value calculated on a basis of event history data of an event that occurs in a second another controller disposed outside the control device; and a memory to store the event history data of the event that occurs during operation of the control device, the first hash value, and the second hash value, wherein the event history data being combined data in which, for each of multiple events that occurs in the control device during operation, a first hash value calculated for a previous event is combined with event data indicating a content of the current event, the event data including the second hash value that is transmitted from the second another controller, the hash value circuitry forms a hash chain by generating a new first hash value on a basis of a latest event history data, and the first hash value stored in the memory is used for verification in verification circuitry that is different from any of the control device, the first another controller, and the second another controller, the verification circuitry comparing the first hash value with a hash value recorded in the first another controller or the second another controller and verifying whether the first hash value is a correct hash value calculated and stored by the control device.

2. The control device according to claim 1 , further comprising anomaly detection circuitry to recalculate the first hash value on a basis of the event history data stored in the memory and detect an anomaly of the recalculated hash value.

3. The control device according to claim 1 , wherein when storing the event history data, the memory stores the event history data and a hash value that is calculated on a basis of event history data of an event that occurs in the control device before the event history data.

4. A controller system, comprising: the control device, the first another controller, and the second another controller according to claim 1 which are configured to communicate with each other.

5. The controller system according to claim 4 , further comprising: a current time management server that manages a current time and includes the first another controller and the second another controller.

6. The controller system according to claim 4 , further comprising: an event history storage server that stores the event history data of the event that occurs during operation of the control device and includes the first another controller and the second another controller.

7. The controller system according to claim 4 , further comprising: the verification circuitry different from any of the control device, the first another controller, and the second another controller, wherein the verification circuitry compares the first hash value with a hash value recorded in the first another controller or the second another controller, and verifies whether the first hash value stored in the memory is a correct hash value calculated and stored by the control device.

8. A controller system, comprising: a plurality of the control devices according to claim 1 which are connected to communicate with each other, wherein the control devices each store the first hash value calculated by the hash value circuitry and a second hash value calculated by a hash value circuitry of at least another one of the control devices.

9. The controller system according to claim 8 , further comprising: verification circuitry different from any of the plurality of the control devices, wherein the verification circuitry compares the first hash value calculated by the hash value circuitry of one of the plurality of the control devices with a hash value recorded in another one of the plurality of the control devices, and verifies whether the first hash value stored in a memory of the one of the plurality of the control devices is a correct hash value calculated and stored by the one of the plurality of the control devices.